Maybe you need to start your own online magazine, something intended as a service to writers, rather than an exploitation of them. Instead of asking for all rights up front, publication in the online magazine could be with limited rights, and then additional rights could be requested for (and at the time of) any subsequent use - for example print editions of "best of" collections and so on.

Of course such an endeavour automatically has all the same problems that we face as writers anyway: how to get noticed. But, maybe, by collecting from different sources it might be a place people would turn to, to discover new writings that they want to follow, and so benefit both writers and itself.